[PATCH RFC v3 02/19] mm: add folio_zero_user stub for configs without THP/HUGETLBFS

["Michael S. Tsirkin" <mst@redhat.com>]

folio_zero_user() is defined in mm/memory.c under
CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS.  A subsequent patch
will call it from post_alloc_hook() for all user page zeroing, so
configs without THP or HUGETLBFS will need a stub.

Add a macro in the #else branch that falls back to
clear_user_highpages(), which handles cache aliasing correctly on
VIPT architectures and is always available via highmem.h.

Without THP/HUGETLBFS, only order-0 user pages are allocated, so
the locality optimization in the real folio_zero_user() (zero near
the faulting address last) is not needed.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/mm.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5be3d8a8f806..541d36e5e420 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4718,6 +4718,9 @@ static inline bool vma_is_special_huge(const struct vm_area_struct *vma)
 				   (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
 }
 
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE && !CONFIG_HUGETLBFS */
+#define folio_zero_user(folio, addr_hint) \
+	clear_user_highpages(&(folio)->page, (addr_hint), folio_nr_pages(folio))
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if MAX_NUMNODES > 1
-- 
MST